MkIndy7
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| posted on 28/8/07 at 10:08 PM |
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Ignition Timing Vs Fueling
Firstly ARRRGGHHH!!!!! Megasquirt is a Nightmare! (lets get the out of the way).
Should how the fuel is delivered make a difference to the Ignition timeing?.
I've had the car running with a 32/36DGAS carb to run the (Injection cam) in and to take it for its MOT so it would be legal to tune the
Megasquirt afterwards.
Driving to the MOT the car was hesitant, so on the way back I gave it 5deg more advance across the whole range and it was much more responcive.
Installed all the Megasquirt and R1 Throttle bodies and had them running but there back fireing like mad and i've had to back the timing off
about 10deg from when it was running well on the carb and about 5 from the base settings I was given.
I'm now puzzled where to go, it starts much better with less advance but then its really hesitant.. altho the fueling is running rich, as low as
10:1 and at V.best 14:1.
I'm just struggeling to know what to alter.. surely in theory with the same cam the ignition timing should be the same... or does the mixture
being overly rich affect it by cooling the flame or something?
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MikeRJ
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| posted on 28/8/07 at 10:25 PM |
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Ignition timing and fueling are intrinsically linked, change one and the other will need to be optimsed.
The primary reason is that a weak mixture burns more slowly than a rich one, and will therefore need more advance.
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Chippy
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| posted on 28/8/07 at 11:03 PM |
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Bite the bullet, and get it to a rolling road, you will be amazed at the change. Mine went from 160bhp to 174, and boy does it make a huge difference.
Ray
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MkIndy7
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| posted on 28/8/07 at 11:10 PM |
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quote:
Originally posted by Chippy
Bite the bullet, and get it to a rolling road, you will be amazed at the change.
 I know but i've spent all that money on a shiney LC-1!
Its all made to sound so easy (just get a LC-1 and it'll tune itself.. yeh right!).. unlike the Megajolt was that was a delight to work with!
Megasquirt really needs a IDIOTS guide written by 1 person that ties in with the software. "alter xxx in the enrichment", Acceleration
enrichment?, temperature enrichment?, VE?, come on give us a clue
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oadamo
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| posted on 28/8/07 at 11:16 PM |
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quote:
Originally posted by MkIndy7
quote:
Originally posted by Chippy
Bite the bullet, and get it to a rolling road, you will be amazed at the change.
I know but i've spent all that money on a shiney LC-1!
Its all made to sound so easy (just get a LC-1 and it'll tune itself.. yeh right!).. unlike the Megajolt was that was a delight to work with!
Megasquirt really needs a IDIOTS guide written by 1 person that ties in with the software. "alter xxx in the enrichment", Acceleration
enrichment?, temperature enrichment?, VE?, come on give us a clue
ive got megasquirt but iam no where near using it yet ive read you log off the lc1 the adjust your map to suit. is that how your doing it because if
its a pain i might just get it rolling roaded and not buy an lc1.
adam
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MkIndy7
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| posted on 28/8/07 at 11:25 PM |
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Form what i've seen of them If you can read the Logs you deserve a Medal.. just a mess of squiggely lines!
Think i'm just grumpy with it at the moment lol.
There are options like "auto tune" in the MS software but as yet they seem to be having little or no effect.
And auto calculating values like how much fuel is required where you put in the CC of the engine and the Injectors CC and it works it out. Mine gives
a figure of 20 (what who knows) and i've now got it down at 8 and its still far too rich certainly at idle and pops, bangs and blows up when you
press the throttle hard!.
There are 2 many things that are poorly described, explained and quantified to be able to understand. I like to know 20 what.. %, cc, mm whatever then
I can grasp it better and rationalise what its doing.
Thats why i'm asking this question really as to weather is Fuel or Ignition related, considering it ran ok on the Carbs on that timeing, and a
range of 10deg either way can't get it back
[Edited on 28/8/07 by MkIndy7]
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garage19
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| posted on 29/8/07 at 06:40 AM |
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quote:
Originally posted by MikeRJ
Ignition timing and fueling are intrinsically linked, change one and the other will need to be optimsed.
The primary reason is that a weak mixture burns more slowly than a rich one, and will therefore need more advance.
Sorry mate, you have that the wrong way round. A rich mixture will burn slower that a lean mixture effectivly moving your peak cylinder pressure
further past TDC.
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MkIndy7
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| posted on 29/8/07 at 06:47 AM |
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I can understand that for peak power the timeing and Mixture can be closely linked.
But where having it where the car even struggles to turn over, and is back fireing out of the TB's on the same and even further retarded maps
than when it was on the carbs.
Surely this can't be caused by how rich its running?
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garage19
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| posted on 29/8/07 at 06:53 AM |
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If you are new to tuning i suggest that you find an ignition map online that is suitable for a pinto with the same cam as you and individual TBs.
Then concentrate on getting the fuelling right.
Your pinto will actually just about run on any mixture between 8:1 and 21:1!!!
Your misfire is probably due to your 10:1 richness, especially if this is lower in the rpm. The spark plug will be having dificulties trying to spark
in that rich mixture.
My advice for a newbie with a n/a engine would be to tune the hole range for 12:5 - 13:1 to get you started.
After you have it running you can then work on your fuel economy and enable closed loop etc.
You can for example run the idle and cruise at 14.7:1 for economy using the closed loop but if you have cams with alot of overlap this may not give
you the strongest idle, you may need richer.
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garage19
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| posted on 29/8/07 at 06:55 AM |
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quote:
Originally posted by MkIndy7
I can understand that for peak power the timeing and Mixture can be closely linked.
But where having it where the car even struggles to turn over, and is back fireing out of the TB's on the same and even further retarded maps
than when it was on the carbs.
Surely this can't be caused by how rich its running?
Certainly can. What AFR and ign advance are you running at idle?
I would imagine a pinto would run about 14/15 degrees at idle.
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MikeRJ
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| posted on 29/8/07 at 08:40 AM |
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quote:
Originally posted by garage19
quote:
Originally posted by MikeRJ
Ignition timing and fueling are intrinsically linked, change one and the other will need to be optimsed.
The primary reason is that a weak mixture burns more slowly than a rich one, and will therefore need more advance.
Sorry mate, you have that the wrong way round. A rich mixture will burn slower that a lean mixture effectivly moving your peak cylinder pressure
further past TDC.
Sorry but weak mixtures burn slower than stoichiometric or slightly rich mixture, fact. This is why running weak mixtures causes exhaust valves to
run so much hotter, without the igntion timing being optimised the mixture is still burning when the exhaust valve opens.
I agree that very rich mixtures also burn more slowly, but you wouldn't normaly be running a normaly aspirated engine at the kind of AFRs where
this makes a big difference.
http://www.innovatemotorsports.com/resources/myths.php
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Syd Bridge
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| posted on 29/8/07 at 09:28 AM |
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As explained to me by a knowledgeable man, very much my senior; A weak mixture tends to 'explode', (oversupply of oxygen) and can be the
cause of detonation, or 'pinging'. A rich mixture 'burns' with a steady flame front. The richer, the slower the flame
front.
At least that's how most of the motor industry that I deal with sees things.
Cheers,
Syd. 
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garage19
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| posted on 29/8/07 at 09:34 AM |
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Agreed very weak mixtures will burn slower but why would you ever want to run your petrol engine that lean? Some manufactures go a bit leaner than
stoich on idle and cruise to squeeze the last drop of economy but thats about it.
In the range of AFRs that you would ever want to run your n/a or forced induction engine on eg 10:1 to 13.5:1 for max power leaner is faster and
richer is slower.
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martyn_16v
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| posted on 29/8/07 at 09:58 AM |
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Yup, weak mixtures burning very slowly are why all ignition systems from the year dot have a 'vacuum advance' for light load running. At
very light load you can need double the advance you will at full throttle.
In theory/ideally tuning fuelling and ignition advance is an iterative process where you keep changing one then the other until you have homed in on
an 'ideal' set of values. However in practice you can get yourself 90% of the way there in far fewer steps. I have had success in the past
by 'calculating' an ignition advance table using the rules of thumb below, and loading that into the MS. I then tune the fuel table until
i'm happy with it (either manually or using the Autotune function) leaving the advance table as it is. Once I have a fuel table i'm happy
with then I start to try tweaking some of the advance values about to see what happens (a quick way to have a poke is to change the 'trim
angle' in the spark settings menu to add/subtract a fixed amount of advance to the whole table and then see where it feels better/worse, keeping
a good ear out for pinking). Once you've made changes you're happy with in the advance table then go back to the fuel and do another quick
round of tuning, you'll likely find it doesn't need much altering so shouldn't take very long.
I find that the VE table generator in Megatune is a bit pants, particularly if you have a relatively high-effort (compared to a lazy american V8) 16v
4cyl where the torque peak rpm is quite close to the peak power rpm, it starts finding really duff values for the lower half of the table.
You're probably better off asking around for a table from a similar engine to start with if you're not happy to tune away from idle from
scratch.
To 'calculate' a starting advance table use this method originally posted on the MSEfi forum a while back...
quote:
The basic principles are to
determine a maximum advance for your engine and work backwards from
there with heuristics:
- older engines (1960s up to 1990 or so) with two valves - max advance = 36°
- newer two-valve engines - max advance = 30°
- three or four valve engines - max advance = 26°
then adjust for bore size:
- under 3.5" (89mm) - subtract 3°
- between 3.5" and 4.000" (101.6mm) - no adjustment
- over 4.001" (+101.6mm) - add 3°
then adjust for the fuel:
- regular - subtract 2°
- mid-grade - subtract 1°
- premium - no adjustment
That gives us a maximum advance figure. It you have an aftermarket
combination with a good squish area and optimized quench, subtract
another 2°. If you have a flathead, add 3° or 4° or more.
We will use this to fill in the table at 100 kPa from 3000 rpm to the redline.
From idle to 3000 rpm, we want the advance (@100kPa) to increase
fairly linearly from the idle advance to the maximum advance. idle
advance is really a matter of tuning, but assume 8° to 16° in most
cases, with stock engines being on the lower end, and 'hotter' engines
being on the upper end.
So if we have a hot engine with 36° maximum advance and 16° idle
advance (at 800rpm), the spark table might look like this for 100kPa:
100 16° 16° 18° 24° 28° 36°
rpm 600 800 1000 1500 2000 3000
Below 100 kPa, we add 0.3° per 1 kPa drop. So for example, if our
total spark at 100kPa and 4000 rpm was 36°, the advance at 50 kPa
would be:
36° + 0.3° x (100-50) = 51°
and the advance at 45 kPa and 800 rpm would be:
16° + 0.3° x (100-45) = 32.5°
However all of these would need to be tuned, and it often helps idle
stability to limit the advance at idle to under 20°.
Finally, for boosted engines, you subtract 0.3° of advance for every
kPa above 100 (it's not a coincidence that this is the same factor as
for the 'vacuum' adjustments). Because 101.3kPa=~14.7psi, this works
out to ~2° per pound of boost. If it often the case that you want to
limit the retard under boost as well, typically so that it takes out
no more than about ½ of the maximum advance at 100 kPa.
there are a couple of spreadsheets that claim to be able to do this for you if you fill in some values
here, you'll have to register/log in to be
able to see the downloads.
[Edited on 29/8/07 by martyn_16v]
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martyn_16v
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| posted on 29/8/07 at 10:06 AM |
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quote:
Originally posted by garage19
In the range of AFRs that you would ever want to run your n/a or forced induction engine on eg 10:1 to 13.5:1 for max power leaner is faster and
richer is slower.
I wouldn't want to run my engine anywhere near 10:1, for a start I can't afford that much petrol and secondly it'll probably be
misfiring by then (and washing all the oil off the bores and killing the engine). You can happily run very lean mixtures of up to about 17:1 at very
light loads, the only reason most manufacturers these days don't stray too far from stoich is that it doesn't do the catalytic converter
any good.
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garage19
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| posted on 29/8/07 at 10:22 AM |
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10: is very rich and can result in bore wash and oil contamination. It was given as an example as a forced induction engine will quite happily run
there under load although not ideal. However some very old 2 valve or side valve engines do have to run suprisingly rich mixtures for max power due to
their poor combustion chamber design.
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MkIndy7
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| posted on 29/8/07 at 11:40 AM |
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quote:
Originally posted by garage19
quote:
Originally posted by MkIndy7
I can understand that for peak power the timeing and Mixture can be closely linked.
But where having it where the car even struggles to turn over, and is back fireing out of the TB's on the same and even further retarded maps
than when it was on the carbs.
Surely this can't be caused by how rich its running?
Certainly can. What AFR and ign advance are you running at idle?
I would imagine a pinto would run about 14/15 degrees at idle.
The engine and ignition ran fine with the Same cam in running on the standard carb,
I'm pretty sure the idle advance was:
10 Deg when going to the MOT,
15 Deg and raised 5 deg through the whole table coming back when it ran better.
I've now tried +/- 5 through the whole table and it still struggles to turn over and back fires sometimes. I just can't fathom why.
The AFR is now running at about 12 at idle and its backfireing worse than when it was at 10 (only backing off the timeing even further helps stop
this but then the car has no power and pops and bangs even worse when trying to drive it)
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martyn_16v
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| posted on 29/8/07 at 01:46 PM |
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Can you post an MSQ here for us to have a look at? (open megatune with MS connected and powered on, and then go to File->Save as... and upload the
file here)
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MkIndy7
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| posted on 29/8/07 at 05:18 PM |
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The MSQ files are on the old laptop and probably very embarassing
The suns shineing outside now so I think i'll attempt another ignition map using the method described above and see if it fairs any better.
Thanks all!
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matt_claydon
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| posted on 29/8/07 at 05:32 PM |
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If you have a working ignition map, stick with it (half the battle is already won if the ignition is sorted!). You fuel map is way out by the sound of
it so you need to concentrate on getting about 14.7:1 around the 'cruise' areas of the map increasing to 12.5:1 in the high-power
areas.
If you've got an LC1 you go out for a 15 minute drive, varying load, rpm, throttle position as much as you can, then run the log through
Megalogviewer with a target AFR table and it will modify your VE table to try to achieve your desired AFRs. Do this a few times and you will have a
good map fairly easily. Only then should you possibly revisit the spark map to see if there are any gains to be had there.
There's loads of info on using Megalog viewer etc on the megasquirt forums and in the mega-manual.
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MkIndy7
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| posted on 29/8/07 at 11:43 PM |
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quote:
Originally posted by matt_claydon
If you have a working ignition map, stick with it (half the battle is already won if the ignition is sorted!). You fuel map is way out by the sound of
it so you need to concentrate on getting about 14.7:1 around the 'cruise' areas of the map increasing to 12.5:1 in the high-power
areas.
If you've got an LC1 you go out for a 15 minute drive, varying load, rpm, throttle position as much as you can, then run the log through
Megalogviewer with a target AFR table and it will modify your VE table to try to achieve your desired AFRs. Do this a few times and you will have a
good map fairly easily. Only then should you possibly revisit the spark map to see if there are any gains to be had there.
There's loads of info on using Megalog viewer etc on the megasquirt forums and in the mega-manual.
Thats what I thought, if the ignition map was sorted that was 1/2 the battle.
Now when its cold, with a water operated R1 choke/air bypass valve it works and starts fine.
But then when warm or under load it Blows back though the TB's and after revving it up it fires out of the exhaust (whilst having a AFR that if
anything is lean upon revving). It even blew the IB's off at 1 point, so must that be Ignition timeing or can that be the result of anything
else?
Tonight after getting the Idle AFR closer to 14 it would idle well at as low as 800rpm but then when hotter and after revving it up with little or no
load so it could "Auto tune" it stalled, and refused to start, only really sluggishly turning over like the ignition timing was completely
wrong?.
So to get it back in the garage I loaded a map that was massively retarded (About 8 deg static and massively lean like 10.5:1) so it would turn over
and drive well enough
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chriscook
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| posted on 31/8/07 at 07:32 AM |
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quote:
Originally posted by MkIndy7
So to get it back in the garage I loaded a map that was massively retarded (About 8 deg static and massively lean like 10.5:1) so it would turn over
and drive well enough
AFR of 10.5 is Rich not Lean (assuming petrol).....
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MkIndy7
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| posted on 31/8/07 at 07:57 PM |
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correct.. I typed it wrong!.
Got on much better with it last night.. had mis-read the bit about starting it with adjusting the REQ_Fuel to get it to start and then putting it
back to the calculated amout once it was started.
Tonights mystery.......
When revved up slowly its fine, do anything sudden like jab the throttle it dies or blipping the throttle rather than a slow build up and it blows out
of the exhaust and sometimes the inlet.. any ideas?
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paulf
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| posted on 31/8/07 at 09:55 PM |
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You need to adjust the accelleration enrichments, but it is best to leave them at a low setting until the fuel map is about correct.
For mapping I have found it best to adjust using the laptop whilst someone else is driving, to get the cruise and light throttle settings about
correct and then use datalogs and megalog viewer to adjust from then on.
The accel enrichment settings seems to be the hardest bit to get correct as to much is as bad as to little and difficult to differentiate between the
two.
Sometimes megalog view gives odd outputs which i then adjust manualy if they seem to far off the rest of the map.
Paul.
quote:
Originally posted by MkIndy7
correct.. I typed it wrong!.
Got on much better with it last night.. had mis-read the bit about starting it with adjusting the REQ_Fuel to get it to start and then putting it
back to the calculated amout once it was started.
Tonights mystery.......
When revved up slowly its fine, do anything sudden like jab the throttle it dies or blipping the throttle rather than a slow build up and it blows out
of the exhaust and sometimes the inlet.. any ideas?
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MkIndy7
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| posted on 31/8/07 at 10:45 PM |
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That was just sat at idle on the drive and then jabbing the throttle etc without actually going anywhere.
If anything the VE table at idle is certainly overfueled, i've had to lean it off to get a KPa of about 60 and a half steady idle.
So you get a base fuel map by driving round really steady and cruising.. and then add features like acceleration enrichments to cater for the odd
situations like suddenly flooring the throttle?
2 things i'm not sure if there helping or hampering, they are R1 Tb's with a water/temperature coke/idle air bypass which seems to do a
good job of speeding up the idle to about 1,000 rpm but when that closes it really dies off to about 600 rpm.. i've started to wind on some
mechanical throttle stop to increase this to around 800 rpm.
Does the TPS need re-calibrating after this?
Also there the TB's with the throttle slides thats have also been mentioned this week, and they hardley seem to open revving it on the drive..
They probably open alot under some serious load, but i'm wondering if they could also cause this sudden wide open throttle stalling.
I am starting to feel slightly more optimistic about all this, and should get a good run at it tomorrow
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